Lithographic apparatus and device manufacturing method

ABSTRACT

A porous member is used in a liquid removal system of an immersion lithographic projection apparatus to smooth uneven flows. A pressure differential across the porous member may be maintained at below the bubble point of the porous member so that a single-phase liquid flow is obtained. Alternatively, the porous member may be used to reduce unevenness in a two-phase flow.

The present application is a continuation of U.S. patent applicationSer. No. 15/293,009, filed on Oct. 13, 2016, now allowed, which is acontinuation of U.S. patent application Ser. No. 14/273,335, filed onMay 8, 2014, now U.S. Pat. No. 9,488,923, which is a continuation ofU.S. patent application Ser. No. 13/223,952, filed on Sep. 1, 2011, nowU.S. Pat. No. 8,755,028, which is a continuation of U.S. patentapplication Ser. No. 12/714,829, filed on Mar. 1, 2010, now U.S. Pat.No. 8,031,325, which is a continuation of U.S. patent application Ser.No. 10/921,348, filed on Aug. 19, 2004, now U.S. Pat. No. 7,701,550, theentire contents of each of the foregoing applications herein fullyincorporated by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective numerical aperature (NA) of thesystem and also increasing the depth of focus.) Other immersion liquidshave been proposed, including water with solid particles (e.g. quartz)suspended therein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see for example U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application no. WO 99/49504, herebyincorporated in its entirety by reference. As illustrated in FIGS. 2 and3, liquid is supplied by at least one inlet IN onto the substrate,preferably along the direction of movement of the substrate relative tothe final element, and is removed by at least one outlet OUT afterhaving passed under the projection system. That is, as the substrate isscanned beneath the element in a −X direction, liquid is supplied at the+X side of the element and taken up at the −X side. FIG. 2 shows thearrangement schematically in which liquid is supplied via inlet IN andis taken up on the other side of the element by outlet OUT which isconnected to a low pressure source. In the illustration of FIG. 2 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible, one example is illustrated in FIG. 3 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element.

SUMMARY

In the immersion lithography arrangements described herein, removal ofan immersion liquid typically involves a two-phase flow—the immersionliquid mixes with ambient gas (e.g., air) or gas from a gas seal used toconfine the immersion liquid. Such a two-phase flow is not very stable,especially when large pressure differentials are used to create stronggas flows to confine the immersion liquid or to ensure that all liquidis collected, and the resulting vibration is undesirable. High pressuregas flows may also cause evaporative drying of liquid remaining on thesubstrate leading to thermal gradients. Gas flows spilling over into thepath of interferometer beams may also affect the accuracy of substratetable position measurements because the interferometer is very sensitiveto changes in the refractive index of the gas in the path of theinterferometer beams, such as may be caused by changes in temperature,pressure and humidity.

Accordingly, it would be advantageous, for example, to provide anarrangement to remove liquid from the vicinity of the substrateeffectively and without generating significant vibration or otherdisturbances.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate using a projection system and havinga liquid supply system arranged to supply a liquid to a space betweenthe projection system and the substrate, comprising a liquid removalsystem including:

-   -   a conduit having an open end adjacent a volume in which liquid        may be present;    -   a porous member between the end of the conduit and the volume;        and    -   a suction device arranged to create a pressure differential        across the porous member.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

-   -   projecting a patterned beam of radiation through a liquid onto a        substrate using a projection system; and    -   removing liquid from a volume by providing a pressure        differential across a porous member bounding at least in part        the volume.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts a liquid removal device according to a particularembodiment of the invention;

FIG. 7 is an enlarged view of part of FIG. 6;

FIG. 8 depicts a liquid supply and removal system according to aparticular embodiment of the invention;

FIG. 8a depicts a variant of the liquid supply and removal system ofFIG. 8;

FIG. 9 depicts a variant of the liquid supply and removal system of FIG.8;

FIG. 10 depicts another variant of the liquid supply and removal systemof FIG. 8;

FIG. 11 depicts still another variant of the liquid supply and removalsystem of FIG. 8;

FIG. 12 depicts a liquid supply and removal system according to anotherparticular embodiment of the invention;

FIG. 13 depicts a variant of the liquid supply and removal system ofFIG. 12;

FIG. 14 depicts a manifold in a liquid removal system according toanother particular embodiment of the invention; and

FIG. 15 depicts a liquid flow regulation system usable in embodiments ofthe invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam PB (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PL configured to project a pattern imparted to the radiation        beam PB by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. An immersion hoodIH, which is described further below, supplies immersion liquid to aspace between the final element of the projection system PL and thesubstrate W.

With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam PB.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe mask MA with respect to the path of the radiation beam PB, e.g.after mechanical retrieval from a mask library, or during a scan. Ingeneral, movement of the mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) themask table MT may be connected to a short-stroke actuator only, or maybe fixed. Mask MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the mask MA, the mask alignmentmarks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-) magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a seal member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table. Such a solution is illustrated in FIG. 5. Theseal member is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). A seal is formedbetween the seal member and the surface of the substrate.

Referring to FIG. 5, reservoir 10 forms a contactless seal to thesubstrate around the image field of the projection system so that liquidis confined to fill a space between the substrate surface and the finalelement of the projection system. The reservoir is formed by a sealmember 12 positioned below and surrounding the final element of theprojection system PL. Liquid is brought into the space below theprojection system and within the seal member 12. The seal member 12extends a little above the final element of the projection system andthe liquid level rises above the final element so that a buffer ofliquid is provided. The seal member 12 has an inner periphery that atthe upper end, in an embodiment, closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the seal member 12 and the surface of the substrate W. The gasseal is formed by gas, e.g. air or synthetic air but, in an embodiment,N₂ or another inert gas, provided under pressure via inlet 15 to the gapbetween seal member 12 and substrate and extracted via first outlet 14.The overpressure on the gas inlet 15, vacuum level on the first outlet14 and geometry of the gap are arranged so that there is a high-velocitygas flow inwards that confines the liquid. Such a system is disclosed inU.S. patent application Ser. No. 10/705,783, hereby incorporated in itsentirety by reference.

FIGS. 6 and 7, the latter of which is an enlarged view of part of theformer, illustrate a liquid removal device 20 according to an embodimentof the invention. The liquid removal device 20 comprises a chamber whichis maintained at a slight underpressure p_(c) and is filled with theimmersion liquid. The lower surface of the chamber is formed of a thinplate 21 having a large number of small holes, e.g. of diameter d_(hole)in the range of 5 to 50 μm, and is maintained at a height h_(gap) in therange of 50 to 300 μm above a surface from which liquid is to beremoved, e.g. the surface of a substrate W. In an embodiment, perforatedplate 21 is at least slightly hydrophilic, i.e. having a contact angleof less than 90° to the immersion liquid, e.g. water.

The underpressure p_(c) is such that the menisci 22 formed in the holesin the perforated plate 21 prevent gas being drawn into the chamber ofthe liquid removal device. However, when the plate 21 comes into contactwith liquid on the surface W there is no meniscus to restrict flow andthe liquid can flow freely into the chamber of the liquid removaldevice. Such a device can remove most of the liquid from the surface ofa substrate W, though a thin film of liquid may remain, as shown in thedrawings.

To improve or maximize liquid removal, the perforated plate 21 should beas thin as possible and the pressure differential between the pressurein the liquid p_(gap) and the pressure in the chamber p_(c) should be ashigh as possible, whilst the pressure differential between p_(c) and thepressure in the gas in the gap p_(air) must be low enough to preventsignificant amounts of gas being drawn into the liquid removal device20. It may not always be possible to prevent gas being drawn into theliquid removal device but the perforated plate will prevent large unevenflows that may cause vibration. Micro-sieves made by electroforming,photoetching and/or laser cutting can be used as the plate 21. Suitablesieves are made by Stork Veco B.V., of Eerbeek, the Netherlands.

FIG. 8 shows a liquid removal device incorporated in a seal member 12 ofand immersion hood IH, according to a particular embodiment of theinvention. FIG. 8 is a cross-sectional view of one side of the sealmember 12, which forms a ring (as used herein, a ring may be circular,rectangular or any other shape) at least partially around the exposurefield of the projection system PL (not shown in FIG. 8). In thisembodiment, the liquid removal device 20 is formed by a ring-shapedchamber 31 near the innermost edge of the underside of the seal member12. The lower surface of the chamber 31 is formed by a porous plate 30,as described above. Ring-shaped chamber 31 is connected to a suitablepump or pumps to remove liquid from the chamber and maintain the desiredunderpressure. In use, the chamber 31 is full of liquid but is shownempty here for clarity.

Outward of the ring-shaped chamber 31 are a gas extraction ring 32 and agas supply ring 33. The gas supply ring 33 has a narrow slit in itslower part and is supplied with gas, e.g. air, artificial air orflushing gas, at a pressure such that the gas escaping out of the slitforms a gas knife 34. The gas forming the gas knife is extracted bysuitable vacuum pumps connected to the gas extraction ring 32 so thatthe resulting gas flow drives any residual liquid inwardly where it canbe removed by the liquid removal device and/or the vacuum pumps, whichshould be able to tolerate vapor of the immersion liquid and/or smallliquid droplets. However, since the majority of the liquid is removed bythe liquid removal device 20, the small amount of liquid removed via thevacuum system does not cause unstable flows which may lead to vibration.

While the chamber 31, gas extraction ring 32, gas supply ring 33 andother rings are described as rings herein, it is not necessary that theysurround the exposure field or be complete. In an embodiment, suchinlet(s) and outlet(s) may simply be circular, rectangular or other typeof elements extending partially along one or more sides of the exposurefield, such as for example, shown in FIGS. 2, 3 and 4.

In the apparatus shown in FIG. 8, most of the gas that forms the gasknife is extracted via gas extraction ring 32, but some gas may flowinto the environment around the immersion hood and potentially disturbthe interferometric position measuring system IF. This can be preventedby the provision of an additional gas extraction ring 35 outside the gasknife, as shown in FIG. 8A.

Because in this embodiment, the liquid removal system can remove most,if not all, of the immersion liquid while at a height of 50 to 300 μmabove the surface of the substrate W or the substrate table WT, lessonerous requirements are put on the seal member vertical position thanwhen a gas bearing is used to confine the immersion liquid. This meansthat the seal member may be positioned vertically with a simpleractuation and control system. It also means that the requirements on theflatness of the substrate table and substrate are reduced, making iteasier to construct devices such as sensors which need to be provided inthe upper surface of the substrate table WT.

Removal of most of the liquid without evaporation also means thattemperature gradients may be reduced, avoiding thermal deformation ofthe substrate, which can lead to printing errors. Evaporation may alsobe further minimized by using humid gas in the gas knife, e.g. with arelative humidity of about 50 to 75%, in combination with a pressuredrop of about 100 to 500 mbar and a flow rate of about 20 to 200 l/min.

Variants of this embodiment of the invention are shown in FIGS. 9 to 11.These variants are the same as that described above except in relationto the shape of the porous plate 30.

As shown in FIG. 9, the porous plate 30 a can be set at a slight angle,so that it is higher at the outside. The increasing gap between theporous plate 30 a and substrate W or substrate table WT with distancefrom the center of the exposure field, changes the shape of the meniscus11 a and helps to ensure that the area that is immersed in liquid has amore or less constant width.

In the variants shown in FIGS. 10 and 11, sharp corners 35 are used tolimit the position of the meniscus 11 a which is held by surface tensionat the sharp corner. The sharp corner can be an obtuse angle, as shownin FIG. 10, or a right angle, as shown in FIG. 11. The shape of the gasextraction ring 32 can be adjusted as necessary.

A seal member according to another particular embodiment of theinvention is shown in FIG. 12, which is a similar view to FIG. 8.

In the embodiment of FIG. 12, a liquid bearing 36 is used to at leastpartially support the seal member 12, in place of separate actuators.The liquid, or hydro-dynamic, bearing 36 is formed by immersion liquidsupplied under pressure to liquid supply chamber 37, in a known manner.The liquid is removed via two-phase extraction chamber 38, which isconnected to suitable pumps (not shown) capable of handling thetwo-phase flow. A gas knife 34 confines the immersion liquid in the samemanner as in previous embodiments.

The use of a liquid bearing 36 enables the seal member 12 to bemaintained at a height of about 50 to 200 μm above the substrate W orsubstrate table WT, easing control and flatness requirements asdescribed above. At the same time, the two-phase extraction reduces thenumber of chambers that need to be formed in the seal member 12 and thenumber of hoses that need to be provided to it.

A porous plate 30 is provided across the bottom of two-phase extractionchamber 38, to control the flow of gas and liquid into it. By suitableselection of the size, number and arrangement of the pores in thisplate, the two-phase flow is made steady, avoiding uneven flow that maycause vibrations. As in the embodiments described above, a micro-sievemay be used as the plate 30.

Also as described in relation to the embodiment above, an inclination ora sharp edge may be provided in the porous plate 30 to control theposition of the meniscus of the immersion liquid 11. Again, the removalof any residual liquid can be effected by a high-humidity, large flowgas knife 34 and the pressure of the gas knife can also be used tocontrol the meniscus position.

In this, and other, embodiments of the invention, the shape of the partof the seal member that is in the immersion liquid may be adjusted toprovide a desired degree of damping of vertical movements of the sealmember 12. In particular, the width L_(da), and hence area, of a part ofthe seal member which confines the liquid 11 into a narrow passage canbe selected to provide the desired damping. The amount of damping willbe determined by the area of the damping region, its height h_(da) abovethe substrate W or substrate table WT, the density ρ of the immersionliquid and its viscosity η. Damping may reduce variations in theposition of the seal member due to vibrations, e.g. caused by unevenfluid flows.

A porous plate 41 may also be used to control the flow in an overflowdrain 40, as shown in FIG. 13. The overflow drain of FIG. 13 may beapplied in any of the embodiments of the invention described herein. Theoverflow drain is provided in an upper surface of the seal member 12 ata relatively large radius from the center of the seal member 12. In casethe space between the final element of the projection system PL and thesubstrate W becomes overfull of immersion liquid, the excess liquid willflow onto the top of the seal member 12 and into the drain 40. The drain40 is normally full of liquid and maintained at a slight underpressure.The porous plate 41 prevents gas being drawn into the overflow drain butallows liquid to be drained away when required. The porous plate mayalso be set at a slight angle to the horizontal.

A porous separator can also be used in a manifold 50 that is provided ina liquid drain system that takes a two-phase flow from the immersionhood IH. As shown in FIG. 14, the two-phase flow 51 is discharged into amanifold chamber 51 in which the liquid and gas separate. The gas isremoved from the top of the manifold by a gas outlet 52 which is kept ata pressure of about −0.1 barg by a suitable vacuum pump and pressurecontroller. A liquid removal pipe 53 extends to near the bottom of themanifold and is closed by a porous plate 54. The liquid removal pipe 53is kept at a pressure below the bubble point of the porous plate 54,e.g. about −0.5 barg, With this arrangement, even if the liquid level inthe manifold drops below the bottom of the pipe 53, no gas will be drawnin to it, preventing any unwanted fluctuation in the pressure of themanifold 50, which might be communicated back to the immersion hood IHand cause a disturbance.

A liquid supply system 60 that may be used in embodiments of theinvention is shown in FIG. 15. It comprises, in series: a source 61 ofimmersion liquid, e.g. a fab supply of ultra pure liquid; a constantflow restrictor 62; a variable flow restrictor 63; and a pressureregulator 64 with an external tap, a variable restriction 65 and aconstant restriction 66, positioned just before the immersion hood IH.The pilot line for the pressure regulator 64 is connected downstream ofthe variable restriction 65 and so the input to the constant restriction66 is at a constant pressure, hence the flow into the immersion hood isat constant pressure and rate.

In a lithographic apparatus, a substrate is held on a substrate holder(often referred to as a pimple plate, burl plate or chuck), whichcomprises a flat plate of the same diameter as the substrate having alarge number of small pimples or burls on its major surfaces. Thesubstrate holder is placed in a recess in the substrate table (mirrorblock) and the substrate placed on top of the substrate holder. A vacuumis developed in the spaces between the substrate table and holder andbetween the holder and substrate so that the substrate and holder areclamped in place by atmospheric pressure above the substrate. The recessin the substrate table is necessarily slightly larger than the substrateholder and substrate to accommodate variations in substrate size andplacement. There is therefore a narrow groove or trench around the edgeof the substrate in which immersion liquid may collect. While there theliquid causes no harm but it may be blown out of the groove by a gasbearing or gas knife in the immersion hood. Droplets on the substrate orsubstrate table that result may cause bubbles when the liquid meniscusunder the immersion hood meets them.

The substrate holder is generally made of a material having a lowthermal coefficient of expansivity, such as Zerodur or ULE. Some suchmaterials are porous and in that case the surface pores are filled in toprevent contaminants becoming trapped there. However, it is proposed toleave the surface pores unfilled around the edge of the substrate holderand/or in a peripheral region. Then, when the substrate holder is usedin an immersion lithography apparatus, the immersion liquid entering thegroove will enter the pores of the substrate holder and not be blown outby the gas bearing or gas knife. If the substrate holder has anopen-celled structure, the immersion liquid that has entered its porescan be removed by the vacuum system that clamps the substrate and holderto the table.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system arranged tosupply a liquid to a space between the projection system and thesubstrate, comprising a liquid removal system including: a conduithaving an open end adjacent a volume in which liquid will be present; aporous member between the end of the conduit and the volume; and asuction device arranged to create a pressure differential across theporous member.

In an embodiment, the liquid removal system is arranged to remove liquidfrom a volume adjacent the space. In an embodiment, the apparatusfurther comprises a member at least partially surrounding the space andwherein the conduit comprises a recess in a surface of the member facingthe substrate, the porous member closing the recess. In an embodiment,the member forms a closed loop around the space and the recess extendsaround the whole of the member. In an embodiment, the member furthercomprises a gas supply circuit having an outlet in a surface facing thesubstrate so as to form a gas knife to remove residual liquid from asurface of the substrate, the gas knife being located radially outwardlyof the recess. In an embodiment, the member further comprises a gasextraction circuit having an inlet located between the recess and thegas knife. In an embodiment, the member further comprises a gasextraction circuit having an inlet located radially outwardly of the gasknife. In an embodiment, the member further comprises a liquid supplycircuit having an outlet in a surface facing the substrate so as to forma liquid bearing to at least partly support the weight of the member,the liquid bearing being located radially inwardly of the recess. In anembodiment, during use, the member is supported at a height above thesubstrate in the range of from 50 to 300 μm. In an embodiment, theapparatus further comprises a member at least partially surrounding thespace and wherein the conduit comprises a recess in a surface of themember facing away from the substrate, the porous member closing therecess. In an embodiment, the liquid removal system comprises aliquid/gas separation manifold and the conduit comprises a pipeextending into a lower part of the manifold. In an embodiment, theporous member has pores having a diameter in the range of from 5 to 50μm. In an embodiment, the porous member is hydrophilic.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through a liquidonto a substrate using a projection system; and removing liquid from avolume by providing a pressure differential across a porous memberbounding at least in part the volume.

In an embodiment, the volume is adjacent a space comprising the liquidthrough which the patterned beam is projected. In an embodiment, themethod comprises removing the liquid from the volume using a recess in asurface, facing the substrate, of a member at least partiallysurrounding the space, the porous member closing the recess. In anembodiment, the member forms a closed loop around the space and therecess extends around the whole of the member. In an embodiment, themethod further comprises supplying gas from a surface facing thesubstrate so as to form a gas knife to remove residual liquid from asurface of the substrate, the gas being supplied at a position radiallyoutwardly of the recess. In an embodiment, the method further comprisesremoving gas from a position between the recess and the position wherethe gas is being supplied. In an embodiment, the method furthercomprises removing gas from a position located radially outwardly of theposition where the gas is being supplied. In an embodiment, the methodfurther comprises supplying liquid from a surface facing the substrateso as to form a liquid bearing to at least partly support the weight ofthe member, the liquid being supplied at a position radially inwardly ofthe recess. In an embodiment, the method comprises supporting the memberat a height above the substrate in the range of from 50 to 300 μm. In anembodiment, the method comprises removing the liquid from the volumeusing a recess in a surface, facing away from the substrate, of a memberat least partially surrounding the space, the porous member closing therecess. In an embodiment, the method comprises removing the liquid fromthe volume through a pipe extending into a lower part of a liquid/gasmanifold comprising the volume.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, where applicable, the invention may takethe form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein.

The present invention can be applied to any immersion lithographyapparatus, in particular, but not exclusively, those types mentionedabove. The immersion liquid used in the apparatus may have differentcompositions, according to the desired properties and the wavelength ofexposure radiation used. For an exposure wavelength of 193 nm, ultrapure water or water-based compositions may be used and for this reasonthe immersion liquid is sometimes referred to as water and water-relatedterms such as hydrophilic, hydrophobic, humidity, etc. may be used.However, it is to be understood that embodiments of the presentinvention may be used with other types of liquid in which case suchwater-related terms should be considered replaced by equivalent termsrelating to the immersion liquid used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1-20. (canceled)
 21. A lithographic projection apparatus, comprising aprojection system configured to project a beam of radiation onto aradiation-sensitive substrate, the projection system comprising a finaloptical element and having a bottom surface; a member to at least partlyconfine a liquid to a space between the final optical element and amovable table and at least part of the member extending underneath thebottom surface, the member comprising a recovery opening facing towardthe movable table, the recovery opening comprising a porous structureconfigured to recover liquid; and an extraction outlet, outward relativeto the space, of the recovery opening, the extraction outlet configuredto exhaust liquid escaping past the recovery opening.
 22. The apparatusof claim 21, wherein the porous structure has a shape extending around apath, in the space, of the beam, the shape comprising a plurality ofsides arranged around the path.
 23. The apparatus of claim 22, furthercomprising an enclosure configured to receive fluid recovered throughthe porous structure, the enclosure configured to separate liquid fromgas in the recovered fluid, the enclosure comprising a further porousstructure.
 24. The apparatus of claim 21, further comprising an inlet,outward relative to the space, of the extraction outlet, configured tosupply a fluid.
 25. The apparatus of claim 21, wherein the at least partof the member defines an aperture through which the pattern can beprojected and the aperture having a plurality of sides.
 26. Theapparatus of claim 21, wherein the porous structure comprises: a firstpart configured to recover fluid, the first part having a surfaceessentially parallel to an upper surface of the movable table; and asecond part configured to recover fluid, the second part having asurface facing toward the upper surface of the movable table, at leastpart of the second part surface being further from the movable tablethan the first part surface.
 27. The apparatus of claim 21, furthercomprising an actuator to displace the recovery opening relative to thefinal optical element.
 28. A lithographic projection apparatus,comprising a projection system configured to project a beam of radiationonto a radiation-sensitive substrate, the projection system comprising afinal optical element and having a bottom surface; a member to at leastpartly confine a liquid to a space between the final optical element anda movable table and at least part of the member extending underneath thebottom surface, the member comprising a recovery opening facing towardthe movable table, the recovery opening comprising a porous structureconfigured to recover liquid; and an inlet, outward relative to thespace, of the recovery opening, the inlet configured to provide a fluidto liquid escaping past the recovery opening.
 29. The apparatus of claim28, wherein the porous structure has a shape extending around a path, inthe space, of the beam, the shape comprising a plurality of sidesarranged around the path.
 30. The apparatus of claim 28, furthercomprising an enclosure configured to receive fluid recovered throughthe porous structure, the enclosure configured to separate liquid fromgas in the recovered fluid, the enclosure comprising a further porousstructure.
 31. The apparatus of claim 28, wherein the porous structurecomprises: a first part configured to recover fluid, the first parthaving a surface essentially parallel to an upper surface of the movabletable; and a second part configured to recover fluid, the second parthaving a surface facing toward the upper surface of the movable table,at least part of the second part surface being further from the movabletable than the first part surface.
 32. The apparatus of claim 28,wherein the at least part of the member defines an aperture throughwhich the beam can be projected and the aperture has a plurality ofsides.
 33. The apparatus of claim 28, wherein the inlet is configured toprovide a gas as the fluid.
 34. A lithographic projection apparatus,comprising a projection system configured to project a beam of radiationonto a radiation-sensitive substrate; a member to at least partlyconfine liquid to a space between the projection system and a movabletable, the member comprising a recovery opening facing toward themovable table, the recovery opening comprising a first porous structureconfigured to recover fluid; and a second porous structure configured toreceive recovered fluid from the first porous structure and configuredto exhaust liquid separately from gas in the recovered fluid.
 35. Theapparatus of claim 34, wherein the second porous structure is locatedin, or on, a structure that protrudes into a cavity.
 36. The apparatusof claim 34, further comprising an outlet configured to exhaust gas ofthe recovered fluid, the outlet located above the second porousstructure.
 37. The apparatus of claim 36, wherein the recovered fluid isreceived into a cavity at a position below the outlet.
 38. The apparatusof claim 34, wherein the second porous structure is configured to removesubstantially only liquid.
 39. The apparatus of claim 34, wherein thefirst porous structure has a shape comprising a plurality of sides andthe shape extends around a path, in the space, along which the beam isprojected.
 40. The apparatus of claim 34, wherein a portion of themember is located between a bottom surface of the projection system andthe movable table and is located underneath the bottom surface, theportion defining an aperture through which the beam can be projected andthe aperture having a plurality of sides.